Plate heat exchangers, PHEs, typically consist of two end plates in between which a number of heat transfer plates are arranged in an aligned manner, i.e. in a stack. In one type of well-known PHEs, the so called gasketed PHEs, gaskets are arranged between the heat transfer plates, typically in gasket grooves which run along edges of the heat transfer plates, edge portions extending between the gasket grooves and the plate edges. The end plates, and therefore the heat transfer plates, are pressed towards each other whereby the gaskets seal between the heat transfer plates. The gaskets define parallel flow channels between the heat transfer plates, one channel between each pair of heat transfer plates, through which channels two fluids of initially different temperatures alternately can flow for transferring heat from one fluid to the other.
The heat transfer plates are typically made by cutting out blanks from sheets or coils of stainless steel and pressing these blanks with a pattern adapted to the intended application of the heat transfer plates. The resulting heat transfer plates typically have corrugated edge portions, i.e. edge portions comprising ridges and valleys, to increase the strength of the individual heat transfer plates and also the stack of heat transfer plates in that the ridges and valleys of the individual heat transfer plates may abut against each other in the stack. Another important function of the corrugated edge portions is to support the gaskets and keep them in place. The blank cutting may result in deformation of the blank edges, which, depending on the type of stainless steel, in turn may result in deformation martensite or deformation hardening of the blank edges. Deformation martensite is very hard and brittle and may therefore cause problem when the blanks are pressed. More particularly, the tensile stress resulting from the pressing may cause cracks in the edge portions of the resulting heat transfer plates due to the deformation martensite, which cracks typically run perpendicularly to the plate edges.